The present invention relates in general to sewing machines and in particular to a new and useful device for pulling out and cutting off the needle and looper thread of a sewing machine, wherein the needle and looper threads are first pulled out by unequal amounts and thereafter cut off.
In a sewing machine for waistband finishing it is already known (Pfaff booklet 381900) to start with the sewing at a certain distance from the head of the waistband and to finish the sewing substantially at the same distance before reaching the end of the waistband. During the sewing operation, the sewing material is fed in a feeding direction over a first delivery roller which is driven by a drive that depends from the machine main shaft. A second drive is provided for the delivery roller which operates independently of the first drive, by which the sewing material is displaced in the sewing intervals by the length of the seam-free zones. On each looper is secured a severing knife, against the cutting edge of which the leg of the needle thread leading to the sewing material is moved about the seam-free zone at the end of the trailing portion of the waistband during the displacement of the sewing material, with the sewing machine standing still. A cutoff device for the looper threads is not provided in this sewing machine. The looper threads must therefore be cut off by hand. To this end the sewing material must be removed by hand in the feeding direction with the pressure foot lifted and the delivery roller raised. This procedure not only delays a new start, but it also causes unnecessary thread consumption.
For the safe formation of the next stitch, after the thread has been cut off, the needle and looper thread must be pulled out by different lengths and only then cut off. If a single cutoff device is provided for needle and looper thread, as for example, in a device according to U.S. Pat. No. 3,345,963, this requirement for thread cutting cannot be met, or the needle and the looper thread must be pulled out with different lengths by a specially designed and fitted guide or by deflecting surfaces (Swiss Pat. No. 416,285).
Another solution consists in providing separate thread pull-out means for needle and looper threads, which would have to perform, however, pull-out movements of different lengths and would have to be accommodated together with their driving means in the space below the needle plate or above the work support plate in the delivery path of the sewing material. Both are impossible, however.